In digital storage, a Medium Error is a class of errors that a storage device can experience, which imply that a physical problem was encountered when trying to access the device.
Locations of medium errors can be either temporary (as in the case of bit rot – there is no damage to the medium, the data was simply lost), or permanent (as in the case of scratching – the physical location is unusable from that point onwards).
Devices can sometimes recover from medium errors, either by retrying or by managing to reconcile the data with the checksum.
If the medium has incurred permanent damage, the device might remap the logical address where the error occurred to a different, undamaged physical location.
This is due to the device retrying and attempting to recover from the error.